Black Knapweed
Centaurea nigra
Washington State Classification
Class B — Control Required (Designated)
Knapweed invasions have many impacts including an increase in production costs for ranchers, degrading wildlife habitat, crowding out desirable forage, decreasing plant diversity, increasing soil erosion rates, and posing wildfire hazards.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Black knapweed is a perennial growing from 1 to 5 feet (20 to 150 cm.) tall. Stems are upright and branched and typically covered in short hairs. It flowers from summer to fall.
Leaves
Basal leaves have leaf stalks and are narrow with widest point near the base of the leaf or with the widest point at the middle. The stem leaves become smaller and narrower moving up the stem and stalkless. Leaf margins slightly toothed or smooth.
Flowers
Flowerheads occur at branch tips. Bracts at base of flowerhead covered with dark brown or black fringed margins up to 3 times as long as the bract. Flowerheads made up of 40 to 100+ purple (or rarely white) flowers.
Fruit & Seeds
Seeds may have short blackish unequal bristles on one end that can fall off.
Impact
Knapweed invasions have many impacts including an increase in production costs for ranchers, degrading wildlife habitat, crowding out desirable forage, decreasing plant diversity, increasing soil erosion rates, and posing wildfire hazards.
Ecology & Spread
Habitat
Black knapweed grows along roadsides, in meadows, pastures and open areas. Please click here to see a county level distribution map of black knapweed in Washington.
Spread Mechanisms
Reproduction
Black knapweed reproduces by seed and can regenerate from the crown as well as by perennial root spread.
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